The present invention broadly relates to electrical resistance welding machines for producing longitudinal seams at workpieces, typically in the form of workpiece bodies which are destacked in the form of blanks or the like from a blank stack, rounded in a forming machine and delivered to welding or electrode rolls by means of a transport device which transports such bodies at the requisite welding speed before reaching the welding rolls. More specifically, the invention relates to a new and improved construction of such transport device for use with welding equipment, especially electrical resistance welders.
With heretofore known resistance welding machines of the previously mentioned type the transport device possesses entrainment members fixedly arranged on a revolving chain, the entrainment members pushing the workpiece bodies. A notable drawback of such prior art transport device resides in the fact that at the deflection locations of the chain the entrainment members which engage with the workpiece bodies strike against the edge of such bodies, producing undersirable notches or indentations at such edges. These indentations can be extremely disadvantageous during the further processing of the workpiece bodies into cans, for instance when connecting the workpiece body which is no longer of cylindrical configuration due to the indentation or notch, with a can end or closure, and the end seal of such produced can can become impaired due to the presence of such indentation or notch.
A further appreciable drawback of the transport device used with heretofore known resistance welding machines resides in the fact that the mutual spacing of the entrainment members at the chain determines the length of the workpiece bodies which can be transported with the chain. The maximum length of the bodies at most can be somewhat smaller than the spacing between adjacent entrainment members, because the entrainment members themselves need a certain amount of space between two neighboring bodies. If, however, there should be processed at the machine considerably shorter bodies, then the workpiece bodies have an appreciably greater spacing from one another, resulting in poor production output of the machine owing to the idle phases of the production brought about by virtue of the larger body spacing. In order to enhance the poor adaptability of such type of machines when converting the production from one size of workpiece body to another, it has heretofore been proposed to use exchangeable chains each having a different mutual spacing of their entrainment members. This requires, however, that whenever the production is altered that there be undertaken a complicated change-over or restructuring of the machine which, in turn, means that there is an interruption in the production at the machine during such time as one transport chain is exchanged for another.
It is furthermore known to employ for the transport of the bodies to the welding rolls two different transport systems which transport the bodies at different feed or conveying speeds. This measure is justified in terms of the need for imparting to the blanks, prior to accomplishing the continuous welding operation, a continuous feed or conveying speed which coincides with the welding speed, yet however before the welding operation the bodies which first are destacked from a blank stack must be rounded in a forming or rounding machine, and owing to the time which is needed to accomplish this operation the bodies must be intermittently transported both to and from the forming machine, and specifically, at a greater feed or transport speed than the welding speed, so that the blank which previously was delivered at the welding speed to the welding rolls can be closed-in or approached by the next following workpiece body. Hence, a transfer of each of the workpiece bodies as a practical matter must be accomplished by transport systems having two different feed or conveying speeds. For use with the second transport system operating at the lower feed speed there has been proposed a device having pivotable or oscillating levers controlled by a cam for introducing the the bodies between the welding rolls. This device is synchronized with the first transport system which possesses exchangeable chains where the entrainment members are spaced differently from one another. Consequently, also with this transport device which is combined from both transport systems there is only attainable a limited adaptability to different sizes of the workpiece bodies during a conversion in the production.